Phosphine- and carbene-ligated silver acetate: easily-accessed synthons for reactions with silylated nucleophiles

The useful synthon tricyclohexylphosphinesilver(I) acetate is easily prepared on gram scale by the reaction of silver(I) acetate and tricyclohexylphosphine in a 1:1 ratio in toluene. (PCy(3))Ag(OAc) (1) reacts with a wide range of silylated nucleophiles (Me(3)Si-X; product with X = N(3), 2; Cl, 3; SCN, 4; 1,2,4-triazol-1-yl, 5; trifluoromethanesulfonate (OTf), 6; SPh, 8; Br, 9) to effect room temperature Ag-X bond formation at the expense of the Ag-OAc bond. All new products were characterized by multinuclear NMR spectroscopies, IR spectroscopy, microanalysis, and X-ray crystallography. X-ray crystallography indicated a variety of coordination geometries at silver(I) are accessible, as di- and tetranuclear complexes were observed in all cases except 1, which forms a three-coordinate, mononuclear complex. In the case of 8, NMR and mass spectrometric data suggest fluxional species of variable nuclearity (but with empirical formula [(PCy(3))Au(SPh)](n)) exist in solution. To provide more definitive evidence of Ag-S bond formation, the ligand 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) was used to synthesize a new starting material, (IPr)AgOAc (10), the Ag-OAc bond of which is amenable to silylation by Me(3)Si-X (complex with X = N(3), 11; Cl, 12; SPh, 14). Complex 14 was characterized crystallographically, and provided definitive evidence for Ag-S bond formation via silylation with PhS-SiMe(3). Me(3)SiBr and Me(3)SiI are also competent in the silylation of 10 to yield 13 and 15, but these compounds were more cleanly synthesized by the reaction of 12 and KBr/KI in a biphasic CH(2)Cl(2)/H(2)O mixture. In a preliminary exploration of reactivity, it was determined that azidosilver(I) complexes 2 and 11 react rapidly and quantitatively with (NO)(SbF(6)) (as was previously demonstrated in a related azidogold(I) system) to yield cationic silver(I) species (detected by mass spectrometry). In acetonitrile solution, ligand rearrangements of these cationic silver(I) species yield cationic bis(phosphine) or bis(carbene) complexes, the identities of which were authenticated by X-ray crystallography.